The invention relates to a global navigation satellite system (GNSS) scheme, and more particularly to an update scheme of a set of transformation information parameters used for GNSS satellite trajectory extension data prediction.
For a GNSS receiver system, one of the most important tasks is to speed up Time To First Fix (TTFF), which is a measure of the time required by the GNSS receiver to acquire enough usable satellite signals and data and calculate a position point (called a fix). Speeding up the TTFF can be achieved by extending or predicting the satellite trajectory orbiting Earth, i.e. extending or predicting the orbit ephemeris. Details of one or more examples of a system for predicting satellite trajectory is described in U.S. Pat. No. 7,786,929, issued Aug. 31, 2010. For the prediction of the satellite trajectory, a set of transformation information parameters is required to achieve the coordinate transformation between a first coordinate system and a second coordinate system. The set of transformation information parameters including polar motion, earth rotation (sidereal-rotation), nutation, and precession is usually assumed to be known for the next several years. After a time period such as several years, the set of transformation information parameters will deviate from the presumed values. Once the set of transformation information parameters has expired and becomes incorrect, satellite trajectory deviations will be generated.